Battery pack with balancing management

ABSTRACT

A battery management system for a battery pack comprising multiple battery modules is disclosed. Each of the battery modules includes multiple battery cells. The battery management system includes multiple first balancing units, multiple first controllers, a second balancing unit including multiple second balancing circuits, and a second controller coupled to the battery modules and the second balancing circuits. The first controllers are operable for controlling the first balancing units to adjust voltages of battery cells in the battery module if an unbalance occurs between the battery cells. The second controller is operable for controlling said second balancing circuits to adjust voltages of said battery modules if an unbalance occurs between battery modules.

CROSS REFERENCE TO RELATED APPLICATION

This Application claims priority to the Chinese patent application,Application Number 201010215983.2, filed on Jun. 25, 2010, which ishereby incorporated by reference.

BACKGROUND

During the past few decades, there has been an increasing interest inelectronic devices, such as power supplies for various applications. Theincreasing demand for power supplies has resulted in the continuousdevelopment of battery packs, e.g., rechargeable battery packs.

A battery pack can consist of multiple battery cells coupled in series.When one of the battery cells is damaged, the lifetime of the batterypack will be shortened. An unbalance between any two of the batterycells can lead to a reduction in battery lifetime. FIG. 1 illustrates ablock diagram of a conventional lead-acid battery pack 100. Thelead-acid battery pack 100 is generally employed in low costapplications due to its simple structure.

The lead-acid battery pack 100 can include multiple battery modules101-104 coupled in series. Each of the battery modules 101-104 canconsist of six battery cells 111-116 and two electrodes 120 and 129.Only a voltage of each battery module can be monitored via the twoelectrodes 120 and 129. Once any of the battery cells 101-106 isdamaged, the entire battery pack 100 will be damaged. An unbalancebetween any two of the battery cells 101-106 can further shorten thelifetime of the lead-acid battery pack 100.

SUMMARY

Embodiments of a battery management system for a battery pack comprisingmultiple battery modules are disclosed. Each of the battery modulesincludes multiple battery cells. In one embodiment, the batterymanagement system includes multiple first balancing units, multiplefirst controllers, a second balancing unit including multiple secondbalancing circuits, and a second controller coupled to the batterymodules and the second balancing circuits. The first controllers areoperable for controlling the first balancing units to adjust voltages ofbattery cells in the battery module if an unbalance occurs between thebattery cells. The second controller is operable for controlling saidsecond balancing circuits to adjust voltages of said battery modules ifan unbalance occurs between battery modules.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the claimed subject matterwill become apparent as the following detailed description proceeds, andupon reference to the drawings, wherein like numerals depict like parts,and in which:

FIG. 1 illustrates a block diagram of a conventional lead-acid batterypack.

FIG. 2A illustrates a block diagram of a battery management system for abattery pack, in accordance with one embodiment of the presentinvention.

FIG. 2B illustrates a structure of a balancing circuit in a batterymanagement system for a battery pack, in accordance with one embodimentof the present invention.

FIG. 2C illustrates a structure of a balancing unit in a batterymanagement system for a battery pack, in accordance with one embodimentof the present invention.

FIG. 3 illustrates a block diagram of a battery management system for abattery pack, in accordance with another embodiment of the presentinvention.

FIG. 4 illustrates a block diagram of a battery management system for abattery pack, in accordance with another embodiment of the invention.

FIG. 5 illustrates a structure of a battery pack, in accordance with oneembodiment of the present invention.

FIG. 6 illustrates a flowchart of operations performed by a batterymanagement system for a battery pack, in accordance with one embodimentof the present invention.

FIG. 7 illustrates a block diagram of elements of an electric vehicle,in accordance with one embodiment of the present invention.

FIG. 8 illustrates a block diagram of a battery management system for abattery pack, in accordance with another embodiment of the presentinvention.

FIG. 9 illustrates a block diagram of a battery management system for abattery pack, in accordance with another embodiment of the presentinvention.

FIG. 10 illustrates a flowchart of operations performed by a batterymanagement system for a battery pack, in accordance with one embodimentof the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentinvention. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims.

Furthermore, in the following detailed description of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, it will berecognized by one of ordinary skill in the art that the presentinvention may be practiced without these specific details. In otherinstances, well known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

In one embodiment, a battery management system for a battery pack caninclude multiple first controllers to sense voltages of multiple batterycells coupled in series and to control multiple first balancing circuitsto adjust the voltages of the battery cells if an unbalance occursbetween the battery cells. If an abnormal condition occurs, the firstcontrollers can take measures to protect the corresponding batterycells. The battery management system can further include a secondcontroller to sense voltages of multiple battery modules coupled inseries and to control multiple second balancing circuits to adjust thevoltages of the battery modules if an unbalance occurs between thebattery modules. Due to the balancing technology used for the batterycells and the battery modules, the battery cells and/or modules areprotected from being damaged. Hence, the economy of the batterymanagement system can be improved and battery lifetime can be extended.

FIG. 2A illustrates a block diagram of a battery management system 200for a battery pack, e.g., a lead-acid battery pack, in accordance withone embodiment of the present invention. Balancing technology is used toincrease the lifetime of the battery pack and to improve the economy ofthe battery management system 200.

In one embodiment, the battery pack can include multiple batterymodules, e.g., 211-216, coupled in series. Each of the battery modules211-216 can further include multiple battery cells, e.g., 3, 4, 5, or 6battery cells. Each battery cell may have a voltage of, for example, 2volts, in which case the voltage of each battery module can be 6 volts,8 volts, 10 volts, or 12 volts, depending on the number of batterycells. The battery pack is coupled to a balancing unit 220. In oneembodiment, the balancing unit 220 can include multiple balancingcircuits 221-226 coupled to the battery modules 211-216. Specifically,the balancing circuit 221 is coupled to the battery module 211, thebalancing circuit 222 is coupled to the battery module 212, etc. Thenumber of the battery cells, the battery modules and the balancingcircuits is not limited and can vary based upon the requirements ofdifferent applications. For brevity and clarity, an example of 12-voltbattery module will be described below in detail.

A controller 230 is coupled to the battery pack, e.g., the batterymodules 211-216, and can monitor parameters, e.g., the voltages and/orthe temperatures, of the battery modules 211-216. In one embodiment, thecontroller 230 can timely sense the voltages of the battery modules211-216 and then calculate the voltage difference between the batterymodules 211-216. The controller 230 can determine if an unbalance occursbased upon the voltage difference. When an unbalance occurs between thebattery modules 211-216, the controller 230 can control thecorresponding balancing circuits to adjust the voltages of theunbalanced battery modules. In one embodiment, the controller 230 canenforce a threshold V_(THM) to determine if an unbalance occurs. If thevoltage difference of the battery modules 211-216 is larger than thethreshold, the controller 230 can determine that there is an unbalance.Then the controller 230 can initiate the corresponding balancingcircuits to control an adjustment of the voltages of the unbalancedbattery modules.

In one embodiment, the voltages of the battery modules 211 and 212sensed by the controller 230 are equal to V_(M1) and V_(M2), e.g., 12.4volts and 12 volts, respectively. If the voltage difference ΔV_(M12)between the battery modules 211 and 212 is larger than the thresholdV_(THM), e.g., 0.1 volts, the controller 230 can determine that there isan unbalance between the battery modules 211 and 212. Under control ofthe controller 230, the balancing circuits 221 and 222 can adjust thevoltages of the battery modules 211 and 212 to balance the batterymodules 211 and 212, e.g., the voltage difference between the batterymodules 211 and 212 is not larger than the threshold V_(THM). In oneembodiment, in a passive mode, the balancing circuit 221 can dischargethe battery module 211 during a discharging period or bypass the batterymodule 211 in a charging period in one or more cycles until ΔV_(M12) isdecreased to the threshold V_(THM). In another embodiment, in an activemode, the energy of the battery module 211 can be transferred to thebattery module 212 via a transformer (not shown) until ΔV_(M12) isdecreased to the threshold V_(THM).

In one embodiment, if the unbalance occurs across multiple batterymodules, the controller 230 calculates the voltage differences betweenthose battery modules and prioritizes the voltage differences. Forexample, a voltage difference with the largest value can be given thehighest priority, and a voltage difference with the smallest value canbe given the lowest priority. If two or more voltage differences havethe same values, these voltage differences can be given the samepriority. Then the controller 230 can adjust the unbalanced batterymodules according to the priority for thermal control purposes. In suchan embodiment, if two or more voltage differences have the samepriority, the controller 230 can control the corresponding balancingcircuits concurrently to adjust the voltages of the unbalanced batterymodules. In another embodiment, if the battery management system 200 hasa cooler or fan to solve the thermal problem, the controller 230 willnot determine and/or provide the priority of the voltage differences andcan adjust all the unbalanced battery modules concurrently.

In one embodiment, an electronic control unit (ECU) 240 is coupled tothe controller 230 via the bus 250 and can process data read from thecontroller 230. The data can include, but is not limited to, thevoltages and/or the temperatures of the battery modules 211-216. The ECU240 is provided with software control for managing the balancing of thebattery pack. The ECU 240 can further display the data, and/or send thedata to other devices (not shown) for further processing. The ECU 240 isoptional. In one embodiment, the ECU 240 is omitted for cost-savingpurposes.

Advantageously, the controller 230 can timely monitor the unbalancebetween the battery modules 211-216 and control the correspondingbalancing circuits to adjust the voltages of the unbalanced batterymodules. Hence, the measures mentioned above can be taken to protect theunbalanced battery modules from being damaged. As a result of thebalancing technology used for the battery modules, the lifetime of thebattery pack can be increased.

FIG. 2B illustrates a structure of a balancing circuit 200B in a batterymanagement system for a battery pack, e.g., a lead-acid battery pack ina passive mode, in accordance with one embodiment of the presentinvention. FIG. 2B is described in combination with FIG. 2A. In oneembodiment, the balancing circuits, e.g., 221-226, in FIG. 2A can employthe structure of the balancing circuit 200B.

In one embodiment, the balancing circuit 200B can include a resistor 281and a switch 282 coupled in series. The balancing circuit 200B can becoupled to one of the battery modules in FIG. 2A. More specifically, aterminal of the resistor 281 can be coupled to a positive terminal ofone battery module and a terminal of the switch 282 can be coupled to anegative terminal of the battery module. The switch 282 can becontrolled by the controller 230.

In one embodiment, a first balancing circuit is coupled to a firstbattery module, and a second balancing circuit is coupled to a secondbattery module. The voltage of the first battery module is larger thanthat of the second battery module and there is an unbalance when thevoltage difference between the first and second battery modules islarger than a threshold. The controller 230 turns on a first switch inthe first balancing circuit and turns off a second switch in the secondbalancing circuit. In a discharging period, a discharging current canflow through a first resistor in the first balancing circuit, and hencethe first balancing circuit can discharge the first battery module untila balance is reached between the first and second battery modules. In acharging period, a bypassing current can flow though the first resistor,and consequently the first balancing circuit can bypass the firstbattery module until a balance is reached between the first and secondbattery modules.

FIG. 2C illustrates a structure of a balancing unit 200C in a batterymanagement system for a battery pack, e.g., a lead-acid battery pack inan active mode, in accordance with one embodiment of the presentinvention. In one embodiment, the balancing unit 200C can include atransformer. FIG. 2C is described in combination with FIG. 2A. In oneembodiment, the balancing unit 200C can act as the balancing unit 220 inplace of the balancing circuits 221-226 in FIG. 2A.

In one embodiment, the balancing unit 200C includes multiple secondarywindings, e.g., 291-296, coupled to multiple switches 291A-296A inseries. Each of the secondary windings 291-296 is coupled to arespective battery module, e.g., one of the battery modules 211-216.More specifically, the secondary winding 291 can be coupled to thebattery module 211 via the switch 291A and the secondary winding 292 andcan be coupled to the battery module 212 via the switch 292A, etc. Thebalancing unit 200C can further include a primary winding 290 coupled toa switch 290A in series. The primary winding 290 can be coupled to thebattery pack via the switch 290A. All of the switches, e.g., 290A-296A,can be controlled by the controller 230.

In one embodiment, a first secondary winding is coupled to a firstbattery module via a first switch, and a second secondary winding iscoupled to a second battery module via a second switch. The voltage ofthe first battery module is larger than that of the second batterymodule and there is an unbalance when the voltage difference between thefirst and second battery modules is larger than a threshold. Thecontroller 230 turns on the first switch and turns off other switchesand hence the energy of the first battery module is stored on the firstsecondary winding. In one embodiment, the controller 230 turns on thesecond switch and turns off other switches and hence the energy on thefirst secondary winding is transferred to the second secondary winding.In another embodiment, the controller 230 turns on the switch 290A andturns off other switches and hence the energy on the first secondarywinding is transferred to the primary winding 290. The energy on theprimary winding 290 can be shared by all of the battery modules 211-216.The processing above can be repeated until a balance is achieved.

FIG. 3 illustrates a block diagram of a battery management system 300for a battery pack, e.g., a lead-acid battery pack, in accordance withanother embodiment of the present invention. Balancing technology isemployed to increase the lifetime of the battery pack and to improve theeconomy of the battery management system 300.

In one embodiment, the battery pack includes multiple battery modulescoupled in series (not shown). FIG. 3 illustrates one of the batterymodules, e.g., a battery module 310. The battery module 310 can furtherinclude multiple battery cells, e.g., 301-306. The battery cells 301-306are coupled to a balancing unit 320. In one embodiment, the balancingunit 320 can include multiple balancing circuits, e.g., 321A-326A, whichcan employ the structure of the balancing circuit 200B in FIG. 2B.Specifically, the balancing circuits 321A-326A can include a resistor,e.g., 311-316, and a switch, e.g., 321-326, coupled in series. Thenumber of the battery cells, the battery modules and the balancingcircuits herein is not limited and can vary based upon the requirementsof different applications. An example of a 2-volt battery cell will bedescribed below in detail.

A controller 330 is coupled to the battery module 310, e.g., the batterycells 301-306, and can monitor parameters, e.g., the voltages and/or thetemperatures, of the battery cells 301-306. In one embodiment, thecontroller 330 can timely sense the voltages of the battery cells301-306 and then calculate the voltage difference between the batterycells 301-306. When an unbalance occurs between the battery cells301-306, the controller 330 can control the corresponding balancingcircuits 321A-326A to adjust the voltages of the unbalanced batterycells. In one embodiment, the controller 330 can enforce a thresholdV_(THC) to determine if an unbalance occurs. If the voltage differenceof the battery cells 301-306 is larger than the threshold, thecontroller 330 can determine that there is an unbalance. Then thecontroller 330 can initiate the corresponding balancing circuits tocontrol an adjustment of the voltages of the unbalanced battery cells.

In one embodiment, the voltages of the battery cells 301 and 302 sensedby the controller 330 are equal to V_(C1) and V_(C2), e.g., 2.1 voltsand 2.0 volts, respectively. If the voltage difference ΔV_(C12) betweenthe battery cells 301 and 302 is larger than the threshold V_(THC),e.g., 0.02 volts, the controller 330 can determine that there is anunbalance between the battery cells 301 and 302. In this condition, thecontroller 330 can control the balancing circuits 321A and 322A toadjust the voltages of the battery cells 301 and 302 until a balancebetween the battery cells 301 and 302 is reached, e.g., the voltagedifference between the battery cells 301 and 302 is not larger than thethreshold V_(THC). In one embodiment, in a passive mode, the balancingcircuit 321A can discharge the battery cell 301 in a discharging periodor bypass the battery cell 301 in a charging period until ΔV_(C12)decreases to the threshold V_(THC). More specifically, in thiscondition, the controller 330 can send a control signal to the switch321 and then the switch 321 is turned on in one or more cycles. Hence, acurrent can flow through the resistor 311 and the switch 321 and as aresult, V_(C1) can be reduced. Once V_(C1) is reduced to achieve abalance between the battery cells 301 and 302, the controller 330 canturn off the switch 321 to stop the discharging or bypassing of thebattery cell 301.

In one embodiment, if the unbalance occurs across multiple batterycells, the controller 330 can calculate the voltage differences betweenthose battery cells and prioritize the voltage differences. Then thecontroller 330 can adjust the unbalanced battery cells according to thepriority for thermal control purposes. If two or more voltagedifferences have the same priority, the controller 330 can control thecorresponding balancing circuits concurrently to adjust the voltages ofthe unbalanced battery cells. In another embodiment, the controller 330will not determine and/or provide the priority of the voltagedifferences and can adjust all the unbalanced battery cells concurrentlyif the battery management system 300 has a cooler or fan to solve thethermal problem.

If an abnormal condition occurs, the controller 330 can generate analert signal, and an electronic control unit (ECU) 340 can read thealert signal via a bus 350. The controller 330 can identify an abnormalcondition that can include, but is not limited to, an over-voltage (OV)condition, an under-voltage (UV) condition, or an over-temperature (OT)condition. When the abnormal condition occurs, the controller 330 cantake certain measures to protect the corresponding battery cell.

In one embodiment, if an OV condition occurs, the controller 330 cancontrol the corresponding balancing circuit to disable the charging ofthe OV battery cell. If an UV condition occurs, the controller 330 cancontrol the corresponding balancing circuit to disable the dischargingof the UV battery cell. If an OT condition occurs, the controller 330can control the corresponding balancing circuit to reduce the chargingor discharging current of the OT battery cell, or even to stop thecharging or discharging of the OT battery cell. The number of thebattery cells with an abnormal condition can vary when the batterymanagement system 300 is in operation. If an abnormal condition occursto multiple battery cells, the controller 330 can control thecorresponding balancing circuits concurrently to further improve theefficiency of the battery management system 300.

The ECU 340 is coupled to the controller 330 via the bus 350 and canprocess data read from the controller 330. The data can include, but isnot limited to, the voltages and/or the temperatures of the batterycells 301-306, and the alert signal indicating an abnormal condition.The ECU 340 is provided with software control for the balancingmanagement of the battery pack. The ECU 340 can further display thedata, and/or send the data to other devices (not shown) for furtherprocessing. The ECU 340 is optional. In one embodiment, the ECU 340 isomitted for cost-saving purposes.

In one embodiment, with reference also to both FIG. 2C and FIG. 3, thebalancing unit 200C can replace all of the balancing circuits includingthe balancing unit 320, e.g., the balancing circuits 321A-326A, in anactive mode. A first secondary winding is coupled to a first batterycell via a first switch, and a second secondary winding is coupled to asecond battery cell via a second switch. The voltage of the firstbattery cell is larger than that of the second battery cell and there isan unbalance when the voltage difference between the first and secondbattery cells is larger than a threshold. The controller 330 turns onthe first switch and turns off other switches and hence the energy ofthe first battery cell is stored on the first secondary winding. In oneembodiment, the controller 330 turns on the second switch and turns offother switches and hence the energy on the first secondary winding istransferred to the second secondary winding. In another embodiment, thecontroller 330 turns on the switch 290A and turns off other switches andhence the energy on the first secondary winding is transferred to theprimary winding 290. The energy on the primary winding 290 can be sharedby all of the battery cells 301-306. The processing above can berepeated until a balance is achieved.

Advantageously, the controller 330 can timely monitor the unbalancebetween the battery cells 301-306 and control the correspondingbalancing circuits to adjust the voltages of the unbalanced batterycells. Hence, the measures mentioned above can be taken to protect theunbalanced battery cells from being damaged. The controller 330 candetect an abnormal condition in the battery cells 301-306 and then cantake the above-mentioned measures to protect each battery cell andextend the battery lifetime. Consequently, the lifetime of the batterypack can be increased.

FIG. 4 illustrates a block diagram of a battery management system 400for a battery pack, e.g., a lead-acid battery pack, in accordance withanother embodiment of the invention. Balancing technology for batterycells and balancing technology for battery modules are used in thebattery management system 400 to extend the lifetime of the battery packand to facilitate the balancing rate if any unbalance occurs. FIG. 4 isdescribed in combination with FIG. 2A, FIG. 2B, FIG. 2C and FIG. 3. Theelements in FIG. 4 labeled similar to those in other figures havesimilar functions.

In one embodiment, the battery pack can include multiple batterymodules, e.g., 411-416. Each of the battery modules can consist ofmultiple battery cells coupled in series (not shown in FIG. 4). Anexample of the battery module 411 will be described below. Each of thebattery cells in the battery module 411 is coupled to a respectivebalancing circuit in a balancing unit 421. In one embodiment, thebalancing unit 421 can employ the structure of the balancing unit 320 inFIG. 3. In another embodiment, the balancing unit 421 can employ thestructure of the balancing unit 200C in FIG. 2C.

A controller 431 is coupled to the battery cells in the battery module411 and can monitor parameters, e.g., the voltages and/or thetemperatures, of the battery cells. The controller 431 can act as afront-end module. When an abnormal condition occurs in one battery cell,the controller 431 can control the corresponding balancing circuit toprotect the abnormal battery cell and generate an alert signal to anelectronic control unit (ECU) 441 via a bus 491. If an abnormalcondition occurs in multiple battery cells, the controller 431 cancontrol the corresponding balancing circuits concurrently to protect thecorresponding battery cells so as to improve the efficiency of thebattery management system 400.

The controller 431 can timely sense the voltages of the battery cells inthe battery module 411. When an unbalance occurs between the batterycells in the battery module 411, the controller 431 can control thecorresponding balancing circuits to adjust the voltage of the unbalancedbattery cells by discharging or bypassing the corresponding batterycells or transferring energy between the corresponding battery cells.

The ECU 441 is coupled to the controller 431 via the bus 491 and canprocess data received from the controller 431. The ECU 441 can furtherdisplay the data. In one embodiment, the ECU 441 can transfer the datato an ECU 480 via a coupler 451 for further processing. The coupler 451is used to isolate the communication between a low-voltage side, e.g.,the ECU 480, and a high-voltage side, e.g., the ECU 441, to protect theECU 480 from being damaged by the higher voltage.

In one embodiment, the controller 431 can be coupled to a battery cellin other battery modules (not shown), e.g., the first battery cell, inthe battery module 412. Hence, the controller 431 can sense the voltagesof the first battery cell in the battery module 412 and the batterycells in the battery module 411 concurrently. If an abnormal conditionoccurs or an unbalance occurs between the first battery cell in thebattery module 412 and the battery cells in the battery module 411, thecontroller 431 can settle this issue using the above-mentioned measures.

In one embodiment, if the unbalance occurs across multiple batterycells, the controller 431 can control the corresponding balancingcircuits to adjust the voltages of the unbalanced battery cellsaccording to a priority of the voltage differences between the batterycells for thermal control purposes. In another embodiment, thecontroller 431 will not determine and/or provide the priority of thevoltage differences and can adjust all the unbalanced battery cellsconcurrently if a cooler or fan is included to solve the thermalproblem. If the abnormal condition occurs to multiple battery cells, thecontroller 431 can take measures as described previously concurrently toprotect the corresponding battery cells so as to improve the efficiencyof the battery management system 400.

The controller 470 is coupled to a balancing unit 460, e.g., multiplebalancing circuits, e.g., 461-466, and can timely sense the voltages ofthe battery modules 411-416. In one embodiment, the balancing circuits461-466 can employ the structure of the balancing circuit 200B in FIG.2B and implement similar functions as previously described herein. Inanother embodiment, the balancing unit 460 can employ the structure ofthe balancing unit 200C in FIG. 2C and implement similar functions aspreviously described herein. When an unbalance occurs between two of thebattery modules 411-416, the controller 470 can control thecorresponding balancing circuits 461-466 to adjust the unbalancedbattery modules. In one embodiment, if the unbalance occurs acrossmultiple battery modules, the controller 470 can control thecorresponding balancing circuits to adjust the voltages of theunbalanced battery modules according to a priority of the voltagedifferences between the battery modules for thermal control purposes. Inanother embodiment, the controller 470 will not determine and/or providethe priority of the voltage differences and can adjust all theunbalanced battery modules concurrently if a cooler or fan is includedto solve the thermal problem.

The ECU 480 is coupled to the controller 470 via a bus 482 and canprocess data read from the controller 470. The ECU 480 can furtherdisplay the data, and/or send the data to other devices (not shown) forfurther processing. Advantageously, balancing technology for the batterycells and balancing technology for the battery modules are employed toincrease the efficiency of the battery management system 400 when anunbalance occurs. Hence, the corresponding battery cells or thecorresponding battery modules are protected against damage.Consequently, the lifetime of the battery pack can be expanded.

The ECUs 441-446, the balancing circuits 461-466, the controller 470,and the ECU 480 included in the battery management system 400 areoptional. In one embodiment, the balancing circuits 461-466 and thecontroller 470 are omitted and the corresponding functions areimplemented by software. For example, the ECU 480 can read data from thecontrollers 431-436 via the ECUs 441-446, and the controllers 431-436can take the measures described above to solve different issues. The bus482 can be omitted in this condition. In another embodiment, the ECUs441-446, the balancing circuits 461-466, the controller 470, and the ECU480 are omitted, and the controllers 431-436 can take the measuresdescribed above to solve different issues.

FIG. 5 illustrates a battery pack 500, e.g., a lead-acid battery pack,in accordance with one embodiment of the present invention. In oneembodiment, the battery management system 200, 300, or 400 is employedfor the battery pack 500. The battery pack 500 can include multiplebattery modules, e.g., 501-506, coupled in series. Each battery modulehas two electrodes. The voltage of each of the battery modules 501-506can be monitored via the two electrodes. For example, the battery module501 can be monitored via electrodes 530 and 531, and the battery module506 can be monitored via electrodes 535 and 536.

In one embodiment, each battery module includes multiple battery cells,e.g., 511-516, coupled in series. Each battery cell has two electrodes.The voltage of each of the battery cells 511-516 can be monitored viathe two electrodes. For example, the battery cell 511 can be monitoredvia electrodes 520 and 521, and the battery cell 516 can be monitoredvia electrodes 525 and 526.

FIG. 6 illustrates a flowchart 600 of operations performed by a batterymanagement system for a battery pack, in accordance with one embodimentof the present invention. FIG. 6 is described in combination with FIG.4.

In block 601, the controllers 431-436 can monitor parameters, e.g., thevoltages and/or temperatures, of the battery cells in the batterymodules 411-416. The controller 470 can monitor parameters, e.g., thevoltages and/or temperatures, of the battery modules 411-416.

In block 610, if an abnormal condition occurs to the battery cells, thecontrollers 431-436 can take certain measures to protect thecorresponding battery cells. If an OV condition occurs, the controllers431-436 can control the corresponding balancing units 421-426 to disablethe charging of the OV battery cells. If a UV condition occurs, thecontrollers 431-436 can control the corresponding balancing units421-426 to disable the discharging of the UV battery cells. If an OTcondition occurs, the controllers 431-436 can control the correspondingbalancing units 421-426 to reduce the charging or discharging current ofthe OT battery cell, or to stop the charging or discharging of the OTbattery cell. Advantageously, the controllers 431-436 can control thecorresponding balancing units 421-426 concurrently to improve theefficiency of the battery management system 400.

In block 620, the controllers 431-436 can calculate the voltagedifferences between the battery cells, e.g., ΔV_(C), and compare ΔV_(C)with a threshold V_(THC). If ΔV_(C) is larger than V_(THC), an unbalanceoccurs. In one embodiment, the controllers 431-436 can control thebalancing circuits in the balancing units 411-416 to adjust the voltagesof the unbalanced battery cells according to a priority of the voltagedifferences for thermal control purposes until a balance is achieved. Inanother embodiment, the controller 431-436 can adjust the unbalancedbattery cells concurrently if a cooler or fan is included to solve thethermal problem.

More specifically, in a passive mode, the corresponding balancingcircuit can discharge the battery cell with the higher voltage in adischarging period or bypass the battery cell with the higher voltage ina charging period in one or more cycles, until ΔV_(C) is decreased tothe threshold V_(THC). In an active mode, the energy of the battery cellwith the higher voltage can be transferred to the battery cell with thelower voltage via a transformer (not shown) until ΔV_(C) is decreased tothe threshold V_(THC).

In block 630, the controller 470 can calculate the voltage differencesbetween the battery modules, e.g., ΔV_(M), and compare ΔV_(M) with athreshold V_(THM). If ΔV_(M) is larger than V_(THM), an unbalanceoccurs. In one embodiment, the controller 470 can control thecorresponding balancing circuits 461-466 to adjust the voltages of theunbalanced battery modules according to a priority of the voltagedifferences for thermal control purposes until a balance is achieved. Inanother embodiment, the controller 470 can adjust the unbalanced batterymodules concurrently if the cooler or fan is included to solve thethermal problem.

More specifically, in a passive mode, the corresponding balancingcircuits can discharge the battery module with the higher voltage in adischarging period, or bypass the battery module with the higher voltagein a charging period, in one or more cycles until ΔV_(M) is decreased tothe threshold V_(THM). In an active mode, the energy of the batterymodule with the higher voltage can be transferred to the battery modulewith the lower voltage via a transformer (not shown) until ΔV_(M) isdecreased to the threshold V_(THM).

Advantageously, balancing technology can be employed to adjust thevoltages of multiple battery cells and/or modules according to apriority of the voltage differences or concurrently to improve theefficiency of the battery management system 400.

FIG. 7 illustrates a block diagram of an electric vehicle 700 (e.g., anautomobile), in accordance with one embodiment of the present invention.FIG. 7 is described in conjunction with the other figures. The electricvehicle 700 can include other well-known components in addition to thoseshown.

In one embodiment, the electric vehicle 700 can include a lead-acidbattery pack 701, a battery management system 702, a controllercircuitry 703 and an engine 704. The lead-acid battery pack 701 is not alimitation; other types of battery pack may be used. A batterymanagement system, e.g., 200, 300, or 400, can be employed as thebattery management system 702. In one embodiment, the battery managementsystem 702 and the lead-acid battery pack 701 can be integrated into asingle integrated circuit (IC). The controller circuitry 703 can controlthe power supply from the lead-acid battery pack 701 to the engine 704.The engine 704 can provide energy to the electric vehicle 700.

Advantageously, the battery management system 702 employs the balancingtechnology to timely balance multiple battery cells and/or multiplebattery modules, and hence the lead-acid battery pack 701 can beprotected from being damaged if an unbalance occurs. Hence, the lifetimeof the lead-acid battery pack 701 can be increased and the reliabilityof the electric vehicle 700 can be enhanced.

FIG. 8 illustrates a block diagram of a battery management system 800for a battery pack, e.g., a lead-acid battery pack, in accordance withanother embodiment of the present invention. An inter-cell controller850 is used to increase the lifetime of the battery pack and reduce thecost of the battery pack. FIG. 8 is described with FIG. 2B.

In one embodiment, the battery pack can include one or more batterymodules coupled in series. In the example of FIG. 8, the battery packcan include two battery modules 841 and 842 coupled in series. Batterymodule 841 can include six battery cells 801-806, and battery module 842can include six battery cells 807-812 as illustrated in FIG. 8. Each ofthe battery cells 801-812 is coupled to a respective balancing circuit.In one embodiment, each of the balancing circuits 821-832 can employ thestructure of the balancing circuit 200B in FIG. 2B. More specifically, abalancing circuit can include a resistor, e.g., 281, and a switch, e.g.,282, coupled in series. The number of battery cells, battery modules andbalancing circuits herein is not limited and can vary based on therequirements of different applications. An example of 2-volt batterycell will be described below in detail.

An inter-cell controller 850 is coupled to the balancing circuits821-832, and the battery cells 801-812 and can monitor parameters, e.g.,the voltages, current and/or the temperatures of the battery cells801-812, control the balancing circuits 821-832 when an unbalancedcondition occurs, and further trigger a protection action when anabnormal condition occurs. In one embodiment, the inter-cell controller850 can monitor the voltages of the battery cells 801-812, and then cancalculate the difference between any two of the battery cells 801-812 inthe battery modules 841 and 842. In this situation, the inter-cellcontroller 850 can determine if an unbalance occurs between any two ofthe battery cells, even if the battery cells are in different batterymodules. As a result, the efficiency of cell balancing can be improved.When an unbalance occurs between any two of the battery cells 801-812,the inter-cell controller 850 can control the corresponding balancingcircuits 821-832 to adjust the voltages of the battery cells. In oneembodiment, the unbalance can be detected by inter-cell controller 850.For example, the inter-cell controller 850 can enforce a thresholdV_(TH1) to determine if an unbalance occurs. If a voltage differencebetween any two cells of the battery cells 801-812 is larger than thethreshold V_(TH1), the inter-cell controller 850 determines that thereis an unbalance. The inter-cell controller 850 can initiate thecorresponding balancing circuit to control an adjustment of the voltagesof the unbalanced battery cells.

By way of example, the voltages of the battery cells 801 in the batterymodule 841 and 807 in the battery module 842 sensed by the inter-cellcontroller 850 are equal to V₁ and V₂, e.g., 2.1 volts and 2.0 volts,respectively. If the voltage difference between the battery cells 801and 807

V₁₂ is larger than the threshold V_(TH1), e.g., 0.02 volts, theinter-cell controller 850 determines that an unbalance occurs betweenthe battery cells 801 and 807. In this condition, the inter-cellcontroller 850 can control the balancing circuits 821 and 827 until abalance between the battery cells 801 and 807 is reached, e.g. thevoltage difference between the battery cells 801 and 807 is not largerthan the threshold V_(TH1). In one embodiment, in a passive mode, thebalancing circuit 821 can discharge the battery cell 801 in adischarging period or bypass the battery cell 801 in a charging perioduntil

V₁₂ decreases to the threshold V_(TH1). Each of the balancing circuits821-832 can employ the structure of the balancing circuit in FIG. 2B.The inter-cell controller 850 can send a control signal to the switch282 included in the balancing circuit 821 and the switch 282 in thebalancing circuit 821 can be turned on in one or more cycles. Hence, ina discharging period, a discharging current can flow through theresistor 281 and the switch 282 included in the balancing circuit 821.As a result, V₁ can be reduced. In a charging period, a charging currentcan flow through the resistor 281 and the switch 282 included in thebalancing circuit 821. Once

V₁₂ is not larger than V_(TH1), a balance is achieved between thebattery cells 801 and 807, and the inter-cell controller 850 can turnoff the switch 282 in the balancing circuit 821 so as to stopdischarging or bypassing the battery cell 801.

If the unbalance occurs across multiple battery cells, the inter-cellcontroller 850 can calculate the voltage differences between thosemultiple battery cells and prioritize the voltage differences. In oneembodiment, the largest voltage difference can be given the highestpriority and the smallest voltage difference can be given the lowestpriority and, accordingly, the greater the voltage differences, thehigher the priority. The inter-cell controller 850 can adjust theunbalanced battery cells according to their respective priority. If twoor more voltage differences have the same priority, the inter-cellcontroller 850 can control the corresponding balancing circuitsconcurrently to adjust the voltages of the unbalanced cells. In anotherembodiment, the inter-cell controller 850 will not determine and/orprovide the priority of the voltage differences and can adjust all theunbalanced battery cells concurrently if a cooler or fan is included tosolve the thermal problem.

Moreover, the inter-cell controller 850 can monitor the parameters ofeach of the battery cells 801-812, e.g. current, voltage andtemperature. The inter-cell controller 850 can also detect abnormalconditions including, but not limit to an over voltage (OV) condition,an under voltage (UV) condition, an over temperature (OT) condition, adischarge over current (DOC) condition and a charging over current (COC)condition. If an abnormal condition occurs, the inter-cell controller850 can generate a control signal to turn off a discharge switch 861 inthe lead-acid battery pack and/or generate a control signal to turn offa charge switch 862 in the lead-acid battery pack to terminatedischarging or charging of the battery cells 801-812.

In one embodiment, the inter-cell controller 850 can monitor thevoltages of each of the battery cells 801-812, and compare thesevoltages with the predetermined thresholds V_(OV) and V_(uv) set by theinter-cell controller 850 and determine if an over voltage condition oran under voltage condition occurs. The inter-cell controller 850 canalso monitor the voltage of sense resistor 872, and compare the voltagewith the predetermined thresholds V_(COC) and V_(DOC) set by theinter-cell controller 850 and determine if a charging over currentcondition or a discharge over current condition occurs. The inter-cellcontroller 850 can also monitor the voltage of a thermistor (not shownin the FIG. 8) coupled to each of the cells 801-812 and compare thevoltage with a predetermined thresholds V_(OT) set by the inter-cellcontroller 850 to determine if an over temperature condition occurs. Ifone of these cell voltages is larger than the predetermined thresholdV_(OV), an over voltage (OV) condition occurs, and the inter-cellcontroller 850 can generate a control signal to turn off the chargeswitch 862 to terminate charging of the battery cells 801-812. If one ofthese cell voltages is less than the predetermined threshold V_(UV), anunder voltage (UV) condition occurs, and the inter-cell controller 850can generate a control signal to turn off the discharging switch 861 toterminate discharging of the battery cells 801-812. If the voltage ofsense resistor 872 is larger than the predetermined threshold V_(COC)during a charging period, then a charging over current (COC) conditionoccurs, and the inter-cell controller 850 can generate a control signalto turn off the charging switch 862 to terminate charging of the batterycells 801-812. If the voltage of sense resistor R1 is larger than thepredetermined threshold V_(DOC) during a discharging period, a dischargeover current (DOC) condition occurs, and the inter-cell controller 850can generate a control signal to turn off the discharging switch 861 toterminate discharging of the battery cells 801-812. If the voltage ofthermistor is larger than the predetermined threshold V_(OT), an overtemperature (OT) condition occurs, and the inter-cell controller 850 cangenerate a control signal to turn off the discharging switch 861 and/orthe charging switch 862 to terminate discharging and/or charging of thebattery cells 801-812.

Advantageously, the inter-cell controller 850 can monitor the unbalancebetween the battery cells 801-812 in the battery pack, calculate thedifference between any two of the battery cells 801-812 even indifferent battery modules, and control the corresponding balancingcircuits to adjust the voltages of the unbalanced battery cells.Furthermore, the inter-cell controller 850 can detect abnormalconditions occurs to the battery cells 801-812 and generate a controlsignal to turn off the discharge switch 861 and/or the charge switch 862to terminate discharging and/or charging of the battery cells 801-812for protecting the battery cells from damaged. Consequently, the batterylifetime of the battery pack can be increased.

FIG. 9 illustrates a block diagram of a battery management system 900for a battery pack, e.g., a lead-acid battery pack, in accordance withanother embodiment of the invention. FIG. 9 is described in combinationwith FIG. 2B and FIG. 3.

In one embodiment, the battery pack can include multiple batterymodules. In the example of FIG. 9, a battery module including sixbattery cells 901-906 coupled in series is shown. Each of the batterycells 901-906 can be coupled to one of the balancing circuits 921A-926A.A controller 930 can be coupled to the battery cells 901-906 and thebalancing circuits 921A-926A and can monitor the parameters, e.g., thevoltages of the battery cells 901-906. Elements that are labeled thesame as in FIG. 3 have similar functions and will not be repetitivelydescribed herein.

In one embodiment, an over voltage (OV) detection circuit 960 can becoupled to the terminals of the battery module and can monitor thevoltage of the battery module in the battery pack. The OV detectioncircuit 960 also can be coupled to a module OV balancing circuit 962that is coupled to the terminals of the battery module. In oneembodiment, the module OV balancing circuit 962 can employ the structureof the balancing circuit shown in FIG. 2B to reduce the cost of thebattery pack. More specifically, the module OV balancing circuit caninclude a resistor 281 and a switch 282 coupled in series as shown inFIG. 2B.

In one embodiment, the OV detection circuit 960 can monitor the voltageof the battery module and determine if an over voltage condition occurs.More specifically, the OV detection circuit 960 can set a predeterminedthreshold V_(THOV), e.g., 14.76V, for a battery module of 12 volts. TheOV detection circuit 960 can monitor the voltage of the battery moduleand compare the detected voltage with the predetermined thresholdV_(THOV), and can determine that an over voltage condition occurs whenthe detected voltage is greater than the predetermined thresholdV_(THOV). In response to an over voltage condition, the OV detectioncircuit 960 can generate a control signal to the module OV balancingcircuit 962 to switch on the switch 282 included in the module OVbalancing circuit 962. Thus, a bypass path including the switch 282 andthe resistor 281 can be established between the terminals of the batterymodule. In this situation, the module OV balancing circuit 962 candischarge the battery module when the charging mode is terminated, or itcan bypass the battery module in a charging mode in one or more cyclesuntil the voltage of the battery module is not greater than thepredetermined threshold V_(THOV).

The OV detection circuit 960 can be used to monitor a battery modulethat includes various numbers of battery cells. Accordingly, thepredetermined threshold V_(THOV) can be set based on the number of thebattery cells in a battery module, e.g., 26V for a battery moduleincluding twelve battery cells with battery module voltage of 24 volts.Furthermore, the resistance of the resistor included in the module OVbalancing circuit 962 can be set in accordance with the number of thebattery cells in the battery module to adjust the bypass current so asto improve the efficiency of the battery management system 900.

Advantageously, the module OV balancing circuit 962 can adjust thebattery module voltage, and the balancing circuits 921A-926A can adjustthe voltages of the battery cells in the battery module simultaneously.Thus, the response rate of the battery management system 900 can beincreased, the efficiency of the battery management system 900 can beimproved, and the life time of the battery pack can be increased.

FIG. 10 illustrates a flowchart 1000 of operations performed by abattery management system for a battery pack, e.g., a lead-acid batterypack, in accordance with one embodiment of the present invention. FIG.10 is described in combination with FIG. 9.

In block 1001, the controller 930 can monitor parameters, e.g., thevoltages of the multiple battery cells 901-906 in the battery module,and the OV detection circuit 960 monitors the voltage of the batterymodule V_(M), as illustrated in FIG. 9.

In block 1100, the OV detection circuit 960 can determine if an overvoltage condition occurs. For example, the OV detection circuit 960 canmonitor the battery module voltage V_(M) and compare V_(M) with apredetermined threshold V_(THMOV). When the battery module voltage V_(M)is greater than the predetermined threshold V_(THMOV), an over voltagecondition is detected. The OV detection circuit 960 can control themodule OV balancing circuit 962 to adjust the battery module voltageV_(M). More specifically, the module OV balancing circuit 962 candischarge or bypass the battery module until the battery module voltageV_(M) is decreased to the predetermined threshold V_(THMOV). Moreover,the predetermined threshold V_(THMOV) can be set in accordance with thenumber of the cells in the battery module so that the over voltagecondition can be detected regardless of the number of the cells in thebattery module, and the resistance of the resistor in the module OVbalancing circuit 962 can also be set in accordance with the number ofthe cells in the battery module, so that the bypass current can beadjusted and the efficiency of the battery management system 900 can beimproved.

In block 1200, the controller 930 can calculate the voltage differencesbetween any two of the multiple battery cells, e.g.,

V_(CELL), and compare the voltage difference

V_(CELL) with a predetermined threshold V_(THCELL). When

V_(CELL) is larger than the predetermined threshold V_(THCELL), anunbalanced condition occurs across the multiple battery cells. Thecontroller 930 can control the corresponding balancing circuits toadjust the voltages of the unbalanced cells.

More specifically, the corresponding balancing circuit can discharge thebattery cell with the higher voltage in a discharging period or bypassthe battery cell with the higher voltage in a charging period in one ormore cycles until the voltage difference V_(CELL) is decreased to thepredetermined threshold V_(THCELL).

Advantageously, multiple balancing circuits and the module OV balancingcircuit can be employed to adjust the voltages of the multiple batterycells and/or modules simultaneously to improve the efficiency of thebattery management system 900.

Accordingly, embodiments in accordance with the present inventionprovide a battery management system for a battery pack such as alead-acid battery pack. The battery management system can includemultiple controllers to sense voltages of multiple battery cells coupledin series and to control multiple balancing circuits to adjust thevoltages of the battery cells if an unbalance occurs between the batterycells. If an abnormal condition occurs to the battery cells, thecontroller can take measures to protect the battery cells. Due to thebalancing technology, the battery cells are protected against damage.Hence, the efficiency of the battery management system can be improvedand battery lifetime can be extended.

The battery management system can further include a controller to sensevoltages of battery modules coupled in series and to control multiplebalancing circuits to adjust the voltages of the battery modules if anunbalance occurs between the battery modules. Due to the balancingtechnology, the battery modules are protected against damage. Hence, theefficiency of the battery management system can be improved and batterylifetime can be extended.

While the foregoing description and drawings represent embodiments ofthe present invention, it will be understood that various additions,modifications and substitutions may be made therein without departingfrom the spirit and scope of the principles of the present invention asdefined in the accompanying claims. One skilled in the art willappreciate that the invention may be used with many modifications ofform, structure, arrangement, proportions, materials, elements, andcomponents and otherwise, used in the practice of the invention, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims and theirlegal equivalents, and not limited to the foregoing description.

1. A battery management system for reduced power consumption balancingof a battery pack comprising a plurality of battery modules, each ofsaid battery modules comprising a plurality of battery cells, saidbattery pack comprising a rechargeable multi-cell battery pack, saidbattery management system comprising: a plurality of first balancingunits, each of said first balancing units coupled to a respectivebattery module; a plurality of first controllers, each of said firstcontrollers coupled to a respective battery module and a respectivefirst balancing unit, wherein said first controllers are operable forcontrolling said first balancing units to adjust voltages of batterycells in said battery module if an unbalance occurs between said batterycells; a second balancing unit comprising a plurality of secondbalancing circuits, each of said second balancing circuits coupled to arespective battery module; and a second controller coupled to saidbattery modules and said second balancing circuits, wherein said secondcontroller is operable for controlling said second balancing circuits toadjust voltages of said battery modules if an unbalance occurs betweenbattery modules.
 2. The battery management system of claim 1, furthercomprising: a plurality of electronic control units, each of saidelectronic control units coupled to a respective first controller,wherein said electronic control units are operable for processing datafrom said first controllers.
 3. The battery management system of claim1, wherein each of said first balancing units comprises a plurality offirst balancing circuits, wherein each of said first balancing circuitsis coupled to a respective battery cell, and wherein each of said firstbalancing circuits comprises: a resistor; and a switch coupled to saidresistor in series and controlled by a corresponding first controller.4. The battery management system of claim 1, wherein if an unbalanceoccurs between a first battery cell and a second battery cell such thata voltage of said first battery cell is larger than a voltage of saidsecond battery cell, then said first controllers turn on a first switchthat is coupled to said first battery cell and to a correspondingresistor and turn off a second switch that is coupled to said secondbattery cell.
 5. The battery management system of claim 1, wherein eachof said first balancing units comprises: a primary winding coupled tosaid battery pack via a first switch; and a plurality of secondarywindings coupled to said battery cells via a plurality of secondswitches, each of said secondary windings coupled to a respectivebattery cell.
 6. The battery management system of claim 1, furthercomprising: an electronic control unit coupled to said second controllerand operable for processing data from said second controller.
 7. Thebattery management system of claim 1, wherein if an abnormal conditionoccurs across a battery cell, a corresponding first controller controlsa corresponding first balancing unit to disable said battery cell. 8.The battery management system of claim 1, further comprising: aplurality of first electronic control units, each of said firstelectronic control units coupled to a respective first controller,wherein said first electronic control units are operable for processingdata from said first controllers; a second electronic control unitcoupled to said second controller and operable for processing data fromsaid second controller; and a plurality of couplers, each of saidcouplers coupled to a respective first electronic control unit and tosaid second electronic control unit, wherein said couplers are operablefor isolating communication between said first electronic control unitsand said second electronic control unit.
 9. The battery managementsystem of claim 1, wherein each of said second balancing circuitscomprises: a resistor; and a switch coupled to said resistor in seriesand controlled by said second controller.
 10. The battery managementsystem of claim 1, wherein if said unbalance occurs between a firstbattery module and a second battery module in which a voltage of saidfirst battery module is larger than a voltage of said second batterymodule, then said second controller turns on a first switch that iscoupled to said first battery module and to a corresponding resistor andturns off a second switch that is coupled to said second battery module.11. The battery management system of claim 1, wherein said secondbalancing unit comprises: a primary winding coupled to said battery packvia a first switch; and a plurality of secondary windings coupled tosaid battery modules via a plurality of second switches, each of saidsecondary windings coupled to a respective battery module.
 12. Thebattery management system of claim 1, wherein if an unbalance occursbetween first battery cells and also an unbalance occurs between firstbattery modules concurrently, then said first controllers control saidfirst balancing units to adjust voltages of said first battery cells,and said second controller controls said second balancing circuits toadjust voltages of said first battery modules. 13-33. (canceled)
 34. Amethod for reduced power consumption balancing of a battery packcomprising a plurality of battery modules, each of said battery modulescomprising a plurality of battery cells, said battery pack comprising arechargeable multi-cell battery pack, said method comprising: monitoringvoltages of said battery cells by a plurality of first controllers;determining if an unbalance occurs based upon voltage differencesbetween said battery cells; controlling a plurality of first balancingunits to adjust said voltages of said battery cells if an unbalanceoccurs between said battery cells; monitoring voltages of said batterymodules by a second controller; determining if an unbalance occurs basedupon voltage differences between said battery modules; and controlling asecond balancing unit to adjust said voltages of said battery modules ifan unbalance occurs between said battery modules.
 35. The method ofclaim 34, further comprising: if an unbalance occurs between a firstbattery cell and a second battery cell in which a voltage of said firstbattery cell is larger than said second battery cell, discharging saidfirst battery cell until a balance is achieved.
 36. (canceled)
 37. Themethod of claim 34, further comprising: if an unbalance occurs between afirst battery cell and a second battery cell in which a voltage of saidfirst battery cell is larger than said second battery cell, transferringenergy from said first battery cell to said second battery cell until abalance is achieved.
 38. The method of claim 34, further comprising: ifan abnormal condition occurs to a battery cell, controlling acorresponding first balancing unit to disable said abnormal batterycell.
 39. The method of claim 34, further comprising: if said unbalanceoccurs between a first battery module and a second battery module inwhich a voltage of said first battery module is larger than said secondbattery module, discharging said first battery module until a balance isachieved.
 40. The method of claim 34, further comprising: if saidunbalance occurs between a first battery module and a second batterymodule in which a voltage of said first battery module is larger thansaid second battery module, bypassing said first battery module in acharging period until a balance is achieved.
 41. The method of claim 34,further comprising: if said unbalance occurs between a first batterymodule and a second battery module in which a voltage of said firstbattery module is larger than said second battery module, transferringenergy from said first battery module to said second battery module inuntil a balance is achieved.
 42. (canceled)
 43. The method of claim 41,further comprising: comparing said voltages of said battery modules witha predetermined threshold to determine if said over voltage conditionoccurs on said battery modules; and setting said predetermined thresholdin accordance with the number of battery cells in a respective batterymodule.
 44. (canceled)